1. Field of the Invention
The present invention relates to a method of milking an animal with a desired milking intensity by a milking machine having at least one teatcup with a teatcup liner and a pulsation chamber, the method comprising applying the teatcup to a teat of the animal, and applying a milking vacuum to the interior of the teatcup liner and a pulsating vacuum to the pulsation chamber so that the teatcup liner cyclically moves between a substantially open and a substantially closed position in a series of pulsation cycles. Moreover the invention relates to a milking machine comprising at least one teatcup having a teatcup liner and a pulsation chamber, a vacuum source for generating a milking vacuum in the interior of the teatcup liner and a pulsator provided to alternately connect the pulsation chamber to the atmosphere and to said vacuum source for generating a pulsating vacuum in the pulsation chamber to produce a pulsating movement of the teatcup liner between a substantially open and a substantially closed position.
2. Description of the Prior Art
Traditionally the milking machine comprises a cluster having a claw and four teatcups, each teatcup having a shell and a teatcup liner provided in the shell to form a pulsation chamber between the teatcup liner and the shell. During milking the interior of the teatcup liner is subjected to a milking vacuum, i.e. a low pressure of normally about 50 kPa under atmospheric pressure. There are also milking machines working under high pressure conditions, whereby the low pressure might be above atmospheric pressure. The pulsation chamber is subjected to a cyclically pulsating vacuum normally varying between atmospheric pressure, when the teatcup liner is collapsed or closed, and a maximum vacuum level when the teatcup liner is fully open. The maximum pulsating vacuum level is normally a low pressure level of 50 kPa under atmospheric pressure, i.e. equal to the milking vacuum level. This means that the pressure difference across the wall of the teatcup liner is essentially equal to zero when the teatcup liner is fully open.
The pulsating vacuum demonstrates a pulsation cycle which may be divided into four phases, i.e. (a) an opening phase during which the pulsating vacuum increases from atmospheric pressure to normally about the milking vacuum level and the teatcup liner moves from a closed position to an open position, (b) an open phase during which the pulsating vacuum has reached its maximum level and is essentially equal to the milking vacuum level and the teatcup liner is in an open position, (c) a closing phase during which the pulsating vacuum decreases from about the milking vacuum level to the atmospheric pressure and the teatcup liner moves from the open position to the closed position, and finally (d), a closed phase during which the pulsating vacuum is equal to the atmospheric pressure and the teatcup liner is in a closed position. The time relations between the open and the closed positions are defined in the pulsator ratio. The opening and the closing of the teatcup liner during phase (a) and (c), respectively comprises a very fast and abrupt movement of the teatcup liner. From a closed position, i.e. opposite wall portions of the teatcup liner touch each other, as the pulsating vacuum increases the teatcup liner remains essentially closed until it at a certain pulsating vacuum level, the so called TPD (touch pressure difference), starts to open abruptly to the so called CCPD (critical collapse pressure difference) at which level the teatcup liner is fully open, i.e. said opposite wall portions of the teatcup liner are spaced apart from each other. From the point of time when the pulsating vacuum exceeds the CCPD-level the teatucp liner thus is essentially open and a further increase of the pulsating vacuum only results in an insignificant further opening of the teatcup liner.
Each milking may be divided into four periods, i.e. (I) the initial stimulation or massage period, (II) the main flow period, (III) the flow decreasing period, and (IV) the flow terminating period. During the initial, flow decreasing and flow terminating period the milk flow is reduced in comparison with the main flow period.
In the prior art many proposals have been made for controlling the milking in response to the milk flow.
WO-A-9 212 625 discloses a method of operating a milking machine such that the pulsating vacuum increase and decrease are changed at a slower rate during the massage period, the flow decreasing period and the flow terminating period. During the main flow period the pulsating vacuum changes at a normal rate. By means of this way of operating the milking machine, the teatcup liner moves more slowly when the milk flow is reduced.
EP-A-584 890 and SE-B-382 547 both relate to the control of the pulsating vacuum in response to the milk flow which is detected by a milk flow sensor. EP-A-584 890 proposes to adjust the pulsator ratio in response to the milk flow such that the closed phase (d) is extended when the milk flow is reduced. SE-B-382 547 proposes to reduce the maximum pulsating vacuum level when the milk flow is less than a certain value.
Milk meters of different types are known. Firstly there are milk meters that count portions of constant weight or volume. Secondly there are milk meters that measure a continuous milk flow. These known devices are expensive and have a complicated structure and are normally only provided on the long milk tube leading the milk away from the teatcup claw. Consequently these devices are only able to measure the amount of milk of the total milk flow from all teatcups in a cluster.
The milk flow from one of the teats of the udder is not identical to the milk flow of the other teats of the udder. This means e.g. that the point of time when the milk flow ceases is different for each teat. This can be seen in a milk flow diagram showing the total milk flow from the udder as a stepwise reduction of the milk flow under the flow decreasing period. Therefore if the milking of an animal is interrupted only when the milk flow from all the teats has ceased, the teats which are subjected to a high milking vacuum although no milk is flowing are treated in a very unsatisfactory manner since the opening movement of the teatcup liner leads to a fast increase of the volume in the interior of the teatcup liner. Such volume increase will result in a momentary increase of the vacuum which may subject the exposed teat surface to a strong vacuum, resulting in stretching of the teat surface, and may lead to a back flow of the milk or milk droplets which are jetted with a very high velocity towards and against the teat tip. This is a rather ungentle treatment which may hurt the animal, lead to injuries on the teats and furthermore the backflow of milk increases the risk of transmitting diseases, e.g. mastitis. It may happen that bacteria associated with one teat passes directly into the interior of another teat, and thereby increasing the risk of infection.
Such a vacuum increase during in particular the terminating period may also result in that the teatcup is crawling upwards on the teat. Such crawling at the end of the milking as the teat becomes slack leads to a throttling of the milk conducting interior of the teat, and consequently the milk flow may be interrupted although a considerable amount of rest milk remains in the udder.
U.S. Pat. No. 4,292,926 aims to improve finish milking and discloses a mechanical milking method, wherein the milk flow is continuously measured during milking and the milking intensity is reduced dependent on the result of the measurement. Alternatively the pressure inside the head of the teat rubber is continuously measured when the milking intensity is abruptly reduced at the start of a drop of said pressure.
U.S. Pat. No. 4,211,184 discloses a method and an apparatus for milking with the aim to minimise vacuum damages to the teats of the animal. This document proposes to monitor the vacuum level in a ring chamber of the mouth piece of the teatcup and to control the pulsating vacuum in response thereto. The disclosed method and apparatus is described to operate such that the full milking vacuum level will be experienced in the ring chamber in the initial period to control the maximum pulsating vacuum to be at a low level, thus closing the teatcup liner, preventing the teatcup liner from crawling and preventing the strong milking vacuum from damaging the teat. At full milk flow the teat will be pressurized by the presence of milk in the teat resulting in a reduced vacuum level in the ring chamber and thus an increase in the maximum pulsating vacuum level. At the flow terminating period the vacuum level in the ring chamber will again increase, which once again reduces the maximum pulsating vacuum level.
WO-A-9 314 625 discloses a milking apparatus including for each claw a pulsator and a control unit responsive to the opening and closing of the teatcup liners. The pulsating switching characteristics of the pulsator are controlled by the control unit in sympathy with the opening and closing of the teatcup liners in order to improve the pulsation effectiveness, i.e. to ensure the fully collapsing and opening of the teatcup liner in a single pulsation cycle. Thus this piece of prior art provides a method in which the pulsator is not switched from the atmospheric pressure to a low pressure or vice versa until the liner is fully closed or opened, respectively. When the liners are fully closed or opened, the air flow in the pulsating vacuum pipe ceases. This cessation of air flow is detected by different means porposed in WO-A-9 314 625. For example such means comprises a piston and a cylinder device provided in the pulsating vacuum pipe, whereby the piston moves with the air flow and comes to rest at two opposite positions at which positions the piston is detected to give a signal to the pulsator to change between atmospheric pressure and low pressure. Other proposed means are a device comprising a rubber diaphragm moving in response to air flow, a rotating turbine device, and a hot wire galvanometer. None of the devices proposed in this document is provided to detect the opening or closing movement of the teatcup liner until this movement has already occurred. Moreover the detection of the completed movement is merely used for ensuring the fully opening and closing, respectively of the teatcup liner. Thus all the detecting devices proposed are directly connected to the pulsator only to influence the point of time for switching the pulsator between low pressure and atmospheric pressure varying with the movement of the teatcup liner.